Susan it is not the same thing :have a look at the site given by Lori
Thank you Lori;I had seen those:good explanation
Maggi,heat storage is not enough to maintain the greenhouse frostfree if there are several consecutive frosty cloudy days.But the air coming from the pipes is at about 10°c in the winter,a bit more in the summer,so then it can also be used for cooling.
My back is as bad as yours so I used a JCB to dig the hole and I can borrow a minidigger to dig the trenches.
But I have no idea how long to make them and how many.
There is(was?) a site of somebody who had done that,located in a "cold"state of USA and was able to grow oranges in his greenhouse but I can't find it back.He also used the system to heat his house with the help of a heatpump.